Natural resources such as gas, oil, and water residing in a subterranean formation or zone are usually produced by drilling a well bore into the subterranean formation while circulating a drilling fluid in the well bore.
After a portion of the wellbore is drilled, sections of steel pipe, referred to as casing, which are slightly smaller in diameter than the borehole, are placed in at least the uppermost portions of the wellbore. The casing provides structural integrity to the newly drilled borehole.
Cementing is a common well operation. For example, hydraulic cement compositions can be used in cementing operations in which a string of pipe, such as casing or liner, is cemented in a wellbore. The cement stabilizes the pipe in the wellbore and prevents undesirable migration of fluids along the annulus between the wellbore and the outside of the casing or liner from one zone along the wellbore to the next. Where the wellbore penetrates into a hydrocarbon-bearing zone of a subterranean formation, the casing can later be perforated to allow fluid communication between the zone and the wellbore. The cemented casing also enables subsequent or remedial separation or isolation of one or more production zones of the wellbore by using downhole tools, such as packers or plugs, or by using other techniques, such as forming sand plugs or placing cement in the perforations. Waste disposal wells also benefit from primary cementing with resins due to their greater chemical and acid resistance than cement.
Secondary or remedial cementing operations may also be performed, for example, to repair a primary cementing or treat conditions within the well bore after the well bore has been constructed.
A variety of treatment fluids, including non-cementitious sealants, such as polymer-based, resin-based, or latex-based sealants, have been used in these secondary or remedial cementing operations. These compositions may be introduced and circulated through the well bore to plug a void or crack in the conduit or cement sheath or an opening between the two. In addition, such non-cementitious sealants may have other uses or applications in a well.
Proper placement of a setting composition is possible by controlling the density of the cement or resin. The desired density for a cement or resin is dependent on the well conditions. In general, but not always, lighter density resin systems are typically used in surface casing and higher density resin systems are generally used in deeper parts of the wellbore.
The control of resin density is critical for a successful well construction or remediation. To help control the density of a settable sealant composition, particulate weighting agents, such as barite (BaSO4), sand, hematite, or silica flour, can be used, including for resin systems. However, in some slow curing formulations, dispersions of these weighting agents in resin can become physically unstable due to thermal thinning of resins. This instability manifests itself by settling of the weighting agent in the resin during curing resulting in a resin system with a density gradient rather than homogeneous density throughout. This problem is most pronounced in systems without curing accelerator as the resin requires prolonged thickening times.
Amongst many uses for epoxy resins, applications in the oil and gas industry are unique in their demand for long resin pot life and controlled density.